The traditional implantable cardiac pacemaker includes a pulse generator device to which one or more flexible elongate lead wires are coupled. The device is typically implanted in a subcutaneous pocket, remote from the heart, and each of the one or more lead wires extends therefrom to a corresponding electrode, coupled thereto and positioned at a pacing site, either endocardial or epicardial. Mechanical complications and/or MRI compatibility issues, which are sometimes associated with elongate lead wires and well known to those skilled in the art, have motivated the development of implantable cardiac pacing devices that are wholly contained within a relatively compact package for implant in close proximity to the pacing site, for example, within the right ventricle RV of the heart. With reference to FIG. 1, such a device 100 is illustrated, wherein an hermetically sealed housing 105, preferably formed from a biocompatible and biostable metal such as titanium, contains a pulse generator, or an electronic controller (not shown), to which at least one electrode 111 is coupled, for example, by a hermetic feedthrough assembly (not shown) like those known to those skilled in the art of implantable medical devices. Housing 105 may be overlaid with an insulative layer, for example, medical grade polyurethane, parylene, or silicone.
FIG. 1 illustrates device 100 having been deployed out from a distal portion of a standard guiding catheter 150, which has been maneuvered up through the inferior vena cava IVC and into the right ventricle RV from the right atrium RA, according to methods known in the art of interventional cardiology. FIG. 1 further illustrates housing 105 including a tether attachment structure 122 to which an elongate tether 36 is secured; tether 36 is shown extending from device 100 and into catheter 150, so that a proximal end of tether 36 (not shown), which extends out from a proximal end of catheter 150, is accessible to an operator. The operator may tug on tether 36 to test the fixation of device 100 at the implant site, and, if necessary, apply a greater force to tether 36 to remove device 100 from the implant site for repositioning at a more suitable site. But, if satisfied with the performance of device 100 at the illustrated implant site, the operator may release tether 36 from attachment structure 122 and withdraw tether through catheter 150. Although catheter 150 may be adequate, improved tools, which increase the ease of deploying a relatively compact implantable device, like device 100, are desired.